This invention relates to SZ-twisting machines for electric cables in general and more particularly to the mechanical design of a two-stage twisting device, in which a guidance system consisting of guide pulleys for guiding the material to be twisted is arranged at the transition from the first to the second twisting stage.
Two-stage twisting machines are used primarily in the manufacture of communication cables for the combined twisting of conductors to form several twisting units such as pairs, triplets or quads and of the twisting units to form a bundle. It is customary in such a case to arrange the SZ-twisting devices which are working in parallel in the first twisting stage radially with respect to the machine axis, particularly in a concentric distribution about the machine axis. The rotating twisting heads provided at the input and output of the individual SZ-twisting devices are arranged in respective frames which also support the drive devices for the twisting heads. At the transition from the first to the second twisting stage, a special guidance system which consists of guide pulleys and guides each twisting unit up into the vicinity of the machine axis and therefore up into the vicinity of the twisting closer of the second twisting stage is provided.
With regard to each twisting unit, this guidance system consists of at least two guide pulleys which are provided with a guidance groove and are staggered, where the running surface of the innermost guide pulley is approximately tangent to the second twisting stage ("Wire Journal" February, 1978, pages 74 to 79, FIG. 7; Bulletin "Nachrichtenkabel-SZ-Verseilmaschinen", of the firm Frisch, Germany). If ten or more SZ-twisting devices are arranged operating in parallel in the first twisting stage, a very crowded design of the guide pulleys is necessary at the transition from the first to the second twisting stage in order to ensure free paths as short as possible for guiding the twisting units (giving consideration to the undesired untwisting of the reversal points of the twist direction). On the other hand, enough space must be provided so that equipment problems in the area of the guidance system can be corrected.
Starting from a two-stage twisting device of the type described above, it is an object of the present invention to provide a mechanical design of the first twisting stage and the guidance system arranged between the two twisting stages in such a manner that even with more than ten SZ-twisting devices arranged for parallel operation in the first twisting stage (multiple SZ-device) ease of operation of the multiple SZ-device as well as of the guidance system is provided as well as bringing the twisting units as close as possible to the machine axis and, therefore, as close as possible to the twisting head of the second twisting stage, while keeping transverse dimensions of the multiple SZ-device as small as possible.